In the manufacture of tires, increasing concern is given to lateral and radial force variations existing within the tire. It has been determined that lateral and radial run-out problems or "out of round" problems develop, to a large extent, in the tire press. As is known in the art, a green tire is placed within the tire press or mold and the press is closed as a bladder inflates the green tire and forcefully moves the green tire into contact with the hot tread mold. The inflated green tire is maintained within the press for a period of time sufficient to allow the rubber of the tire to be cured at high temperatures. The tread and outline shape are formed on the tire during the first part of this period.
It is most preferably that the bladder move the green tire into contact with the mold contemporaneous with closure of the mold. It has been found that if certain areas of the tire contact the mold before others, force variation problems may result with the tire. Further, if the tire has contacted the mold prior to mold closure, force variation problems may become existent within the tire. Accordingly, it is most preferable that the green tire expand radially at a uniform rate about the circumference of the tire such that mold contact be substantially instantaneously achieved about the tire circumference. In other words, it is preferred that the green tire "grow" at a uniform rate under bladder pressure and that mold contact be achieved at or slightly after the instant of mold closure.
Heretofore, trial and error approaches have been taken to determine the rate of inflation desired for the green tire, and the rate of closure of the mold. Further, no tests have been derived to determine if force variation problems might be existent within a tire at the mold press stage. Force variation tests and determinations have typically been made after the tire has been completed, by running it on a force variation machine. There are no known methods or apparatus by which a determination can be made at the tire press stage as to force variation or "out of roundness" problems which might have developed within the tire. Accordingly, force variation problems imparted in the tire press stage are not detected until far down the assembly line, well after numerous tires may have experienced the same problem.